Authors

EAST Practice Parameter Workgroup for DVT Prophylaxis

Frederick B. Rogers, MD, FACS
University of Vermont Department of Surgery
Director of Trauma and Critical Care
Fletcher Allen Heath Care
Burlington, VT

Mark D. Cipolle, MD, Ph.D.
Surgical Practice Center
Allentown, PA

George Velmahos, MD, Ph.D.
Department of Surgery, Division of Trauma and Critical Care
University of Southern California
Los Angeles, CA

Grace Rozycki, MD
Emory USM, Department of Surgery
Atlanta, GA

I. Statement of the Problem

A number of factors have been reported to increase the risk for venous thromboembolism (VTE) after injury. Because VTE prophylaxis is associated with complications, it is essential to identify subgroups of trauma patients in whom the benefit of VTE prophylaxis will outweigh the risk of its administration. This concept becomes even more important, as the benefit from the different methods of prophylaxis is still unclear when compared to no prophylaxis. Because the literature is inconsistent, a systematic review is needed to produce the best available evidence.

II. Process

Three literature databases were searched (MEDLINE, EMBASE, and Cochrane Controlled Trials Register) for articles reporting on risk factors of VTE. All articles were reviewed by two independent reviewers and a third reviewer in cases of disagreement. The review was done against predetermined screening criteria, and the articles were given a numerical quality score. From an initial broad research that identified 4,093 relevant titles, 73 articles met all the inclusion criteria and were finally accepted for meta-analysis.

Pooled effect sizes (odds ration [OR] and their 95% confidence intervals [CI]) were estimated by the DerSimonian and Laird random-effects model. Shrinkage graphs were produced to display the effect size of each study and compare it with the overall model estimate. The heterogeneity among studies was tested by the Q-statistic and P value for the chi-square test of heterogeneity. A level of significance at P < 0.05 was used for all comparisons.

In order to include a risk factor for meta-analysis, three or more studies should have reported on the risk factor. Risk factors identified only in one or two studies were not included. The risk factors identified were treated as either dichotomous or continuous variables, as appropriate. For instance, if three or more studies provided data on the incidence of VTE in patients who were older or younger than 55 years old, then the risk factor was “age > 55”, a dichotomous variable. On the other hand, if three or more studies provided data on the age of patients with or without VTE by using only a mean and standard deviation, the risk factor was simply “age”, a continuous variable.

III. Recommendations

A. Level I

Patients with spinal cord injuries or spinal fractures are at high risk for venous thromboembolism following trauma.

B. Level II

1 Older age is an increased factor for venous thromboembolism but it is not clear at which exact age the risk increases substantially.

2 Increasing ISS and blood transfusion do appear to be associated with a high risk of venous thromboembolism in single institution studies, however, on meta-analysis these factors did not prove of major significance.

3 Likewise traditional risk factors such as long bone fractures, pelvic fractures or head injuries in many studies may constitutes a high risk patient population in single institution studies but on meta-analysis it did not prove of major significance.

IV. Scientific Foundation

Risk factors as dichotomous variables

The following variables were reported in 3 or more studies and for this reason included in the meta­analysis: gender,^[1-4] head injury,^{[3] [5-11]} long-bone fracture,^{[3-8] [11-16]} pelvic fracture,^{[3] [5] [6] [8] [11] [12] [14] [16]} spinal fracture,^{[3] [5-7] [9-12] [14] [16]} and spinal cord injury.^{[5] [11] [12] [14] [16]}A number of studies included age as a risk factor, but the different cut­off points used in each study (age > 30, 40, 50, 55, etc.) did not allow analysis of this variable. The only risk factors found to place the patient at higher risk for development of DVT were spinal fractures (OR: 2.260, 95%

CI: 1.415, 3.610) and even more spinal-cord injury (OR: 3.017, 95% CI: 1.794, 5.381). There was no significant heterogeneity among studies reporting on the different risk factors.

Risk factors as continuous variables

Three continuous variables, i.e. age,^{[4-6] [11] [14] [17]} injury severity score (ISS),^{[3] [6] [8] [11] [14] [17]} and units of blood transfused,^{[3] [8] [17]} were reported in more than 3 studies and for this reason included in the meta-analysis. Compared to patients without deep venous thrombosis (DVT), patients with DVT were significantly older by

8.133+1.504 (95% CI: 5.115, 11.141) years and had a significantly higher ISS by 1.430+0.747 (95% CI: 0.000, 2.924). This statistical difference in ISS was marginal, as shown by the lower limit of the 95% CI, and has minimal clinical significance. The difference in the amount of blood transfused between patients with and without DVT was not statistically significant (1.882+2.815, 95% CI: -3.637, 7.401). There was no heterogeneity among these studies.

V. Summary

The existing evidence supports the presence of two risk factors of post-traumatic VTE: spinal fractures and spinal cord injuries. Older age is an additional risk factor but it is not clear at which exact age the risk increases substantially. There is inadequate literature evidence to support that other frequently reported risk factors, such as long-bone fractures, pelvic fractures or head injuries, really increase the risk for VTE. There is a need for additional research in this area.

VI. Future Investigation

VII. References

1. Waring WP, Karunas RS. Acute spinal cord injury and the incidence of clinically occurring thromboembolic disease. Paraplegia 1991;29:8-16.
2. Spannagel U, Kujath P. Low molecular weight heparin for the prevention of thromboembolism in outpatients immobilized by plaster cast. Semin Thromb Hemost 1993;19 (suppl 1);131-41.
3. Knudson MM, Lewis FR, Clinton A, et al. Prevention of venous thromboembolism in trauma patients. J Trauma 1994;37:480-7.
4. Abelseth G, Buckley RE, Pineo GE, et al. Incidence of deep vein thrombosis in patients with fractures of the lower extremity distal to the hip. J Orthop Trauma 1996;10:230-5.
5. Kudsk KA, Fabian T, Baum S, et al. Silent deep venous thrombosis in immobilized multiple trauma patients. Am J Surg 1989;158:515-9.
6. Velmahos GC, Nigro J, Tatevossian R, et al. Inability of an aggressive policy of thromboprophylaxis to prevent deep venous thrombosis (DVT) in critically injured patients: are current methods of DVT prophylaxis insufficient? J Am Coll Surg 1998;187:529-33.
7. Spain DA, Richardson JD, Polk JR, et al. Venous thromboembolism in the high-risk trauma patient: do risks justify aggressive screening and prophylaxis? J Trauma 1997;42:463-9.
8. Knudson MM, Collins JA, Goodman SB, et al. Thromboembolism following multiple trauma. J Trauma 1992;32:2-11.
9. Dennis JW, Menawat S, Von Thron J, et al. Efficacy of deep venous thrombosis prophylaxis in trauma patients and identification of high-risk groups. J Trauma 1993;35:132-9.
10. Meyer CS, Blebea J, Davis K, Jr, Fowl R, Kempsczinski RF. Surveillance venous scans for deep venous thrombosis in multiple trauma patients. Ann Vasc Surg 1995;9:109-14.
11. Piotrowski JJ, Alexander JJ, Brandt CP, et al. Is deep vein thrombosis surveillance warranted in high-risk patients? Am J Surg 1996;172:210-3.
12. Napolitano LM, Garlapati VS, Heard SO, et al. Asymptomatic deep venous thrombosis in the trauma patient: is an aggressive screening protocol justified? J Trauma 1995;39:651-9.
13. Hill SL, Berry RE, Ruiz AJ. Deep venous thrombosis in the trauma patient. Am Surg1994;60:405-8.
14. Geerts WH, Code KJ, Jay RM, et al. A prospective study of venous thromboembolism after major trauma. N Engl J Med 1994;331:1601-6.
15. Geerts WH, Jay RM, Code KI, et al. A comparison of low-dose heparin with low-molecular weight heparin as prophylaxis against venous thromboembolism after major trauma. N Engl J Med 1996;335:701-7.
16. Knudson MM, Morabito D, Paiement GD, et al. Use of low molecular weight heparin in preventing thromboembolism in trauma patients. J Trauma 1996;41:446-59.
17. Upchurch GR, Jr, Demling RH, Davies J, et al. Efficacy of subcutaneous heparin in prevention of venous thromboembolic events in trauma patients. Am Surg 1995;61:749-55.

Table 

Evidence Table. Studies reporting on risk factors of venous thromboembolism in trauma patients.